This invention relates generally to material handling and more specifically to conveying and accumulation of work pieces such as boards or cants in a sawmill.
In modern high-speed sawmills, a typical example of an environment where the invention can be applied, logs are typically broken down into a plurality of separate elongated pieces at the machine center known as the primary breakdown system. As logs have been diminishing in size over the years, particularly in the diameter dimension, high-speed systems have necessarily been developed to maintain production and economic requirements. High-speed in-line breakdown processes are necessary; however, at the breakdown stations, separate pieces are simultaneously generated and they must be handled efficiently for further processing.
Typically, the primary breakdown system will generate at least one center cant and side boards, as well as slabs. A center cant is an elongated piece having two flat sides generated by saw lines and two curviliner surfaces being portions of the surface of the log. Cants are then normally directed to a secondary breakdown station where a plurality of individual pieces will be generated, usually having sizes approximating finished lumber sizes. While the cants from the primary breakdown station can continue in line to the secondary cant breakdown station, it is more common for them to undergo a lateral transfer before reaching the secondary cant breakdown station. It is the lateral transfer function where the present invention may be utilized within the sawmill environment.
Side boards are similar to cants in that they normally have two flat surfaces and two curvilinear surfaces, although they are generally thinner and normally proceed to a secondary board breakdown station known as an edger. At the edgers, the side boards are fed linearly through the secondary breakdown system where the two curvilinear side edges are removed either by sawing means or chipping means. The boards flowing out of an edger will usually have a cross-sectional size approximating the finished lumber size. Just as cants normally undergo a lateral transfer from the primary breakdown station, side boards are also transferred laterally to an edging station before being fed linearly through the edger. Slabs, having one flat surface and one curvilinear surface, can be processed in a manner similar to cants and side boards with respect to material handling, specifically via a lateral transfer system to a secondary slab breakdown station where available boards can be generated from the slabs.
A problem in a sawmill in the past has been material handling associated with the high piece counts in the lateral transfer functions. In order to generate maximum production at the primary breakdown station, it is necessary to process the optimum number of logs per unit of time. In modern high-speed mills, piece counts through the primary breakdown system may approach ten per minute. In a typical high-speed facility, if two side boards are generated from each log, the side board material handling and downstream processing system would necessarily be designed to process twenty side boards per minute. Since side boards are elongated and difficult to handle, the piece count needed to be handled is a difficult problem. Oftentimes, with such a high piece count, the boards accumulate too rapidly and overlap, thereby causing pileups, severe skewing and jam-ups. Unscramblers were necessary to attempt to continuously handle the pieces and singulate them for efficient processing at the edger.
In order for the edger to operate at its optimum production capacity, individual side boards must be available continuously at the edger infeed station in a singulated, even-ended and non-skewed orientation. The consequences from inefficient handling in a lateral transfer function are downtime while removing jam-ups and lower productivity through the secondary breakdown stations. Similar problems occurred in the cant lateral transfer function, as well as with the lateral transfer function for slabs. Ideally, side boards, cants and slabs will be available to the infeed station of each respective machine center in a singulated, even-ended and non-skewed orientation on a continuous basis. To ensure such a supply of elongated pieces at each machine center, a crowding and accumulating means is desirable in the lateral transfer function so that on demand there is always a properly oriented piece for movement into the respective machine center. By continuously having an accumulated supply of singulated and properly spaced elongated pieces ahead of each machine center's infeed station, then each machine center can operate at its optimum production capacity.
Accordingly, from the foregoing, it is an object of the present invention to reduce material handling problems in a transfer conveyor.
It is a further object to increase productivity through a downstream processing station.
It is yet another object to increase the productivity of an upstream processing station by reducing downtime from downstream material handling problems.
It is still a further object to provide an accumulation of pieces ahead of a processing station in a proper singulated, even-ended, and non-skewed orientation so that continuous flow can proceed through the processing station.
These and many other objects of the present invention will become apparent upon reading the detailed description to follow in conjunction with the attached drawings.